Single Heterojunction Solar Cell Research Articles

Highly conductive coated wires for interconnection of solar cells with TECC-wire technology

TECC-Wire (thermoplastic and electrically conductive coated wire) represents a promising interconnection technology for temperature sensitive solar cells. TECC-Wire uses round copper wires (160–300 μm) coated with a thermoplastic polymer layer (10–20 μm), filled with electrically conductive particles. This study presents a new wire coating formulation based on a polyamide-type wire enamel (Voltatex® 8609 ECO, melting temperature 180 °C), filled with 12 vol% silver resulting in a conductivity of 480 S/cm. Single half-cut M6 heterojunction (SHJ) solar cells were contacted with the manufactured wires using a laboratory scale stringing machine. Peel tests were performed to characterize the adhesion of the wires to the cell surface, module performance was evaluated using electroluminescence (EL) imaging and current-voltage (IV) measurements, damp heat (DH) tests were used to evaluate the long-term stability of the modules. The wires adhere well to the cells with a peel force of more than 1.5 N/mm, and the highly conductive coating has proven to be robust when contacted with different pressure, which might be beneficial for a reliable high throughput solar module production. The obtained fill factor FF = 81.25 ± 0,12 % is similar to those achieved for solar modules connected via standard soldering techniques IEC standard DH tests confirmed that, the modules exhibiting a power loss of less than 5 % after 1000 h of storage at +85 °C and 85 % relative humidity. These results are very encouraging for further development of the technology towards a low temperature, solder-free, low cost and robust cell interconnection technology.

A A highly efficient InGaP thin film solar cell structure, optimization and characteristics

Inorganic solar cells based on III-V semiconductor materials are widely used owing to their high efficiencies. In this work, we aim to improve the performance of the single heterojunction solar cell InGaP. The InGaP cell is constituted of a back surface field (BSF), a base, an emitter and a window layer with InAlAsP material. The simulation is done after optimization, modeling, and choice of the used materials and the thickness of different layers constituting the solar cell. The choice of materials whose gap energy is decreasing allows the absorption of the solar spectrum in its almost totality. Then, we varied the temperature to know its effects on the gap energy and the efficiency of the InGaP cell. The InGaP and solar cell with optimal parameters are illuminated by an AM1.5 solar spectrum through InAlAsP window layer. The simulation and optimization at 300K of short circuit current parameters (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (?) are done using Tcad Silvaco software. The characteristics obtained are: the minimized thickness of 665 nm, electrical efficiency is about ? = 21.87% for InGaP cell, Jsc = 14.43 mA/cm2, Voc = 1.63 V, and FF = 91.21 %.

Effect of shallow doping on performance parameters of single heterojunction solar cell

Abstract Fill factor and conversion efficiency of single heterojunction solar cell is analytically computed based on the shallow doping at GaAs quantum well region. Poisson’s equation is solved with suitable boundary condition applied at hetero-interface for both dark and illuminated conditions, corresponding to which open-circuit voltage and short-circuit current are computed. Realistic dependence of minority carrier distribution on material layers and diffusion widths are taken into account for simulation purpose. Result exhibits that variation of acceptor density leads to better outcome in terms of both efficiency and fill factor, which is also critically depends on length of quantum well region. Doping of AlGaAs barrier layer has negligible influence on fill factor and conversion efficiency. Optimized dimension of quantum well layer width is the critical parameter for design of efficient solar cell, as revealed from the analysis.

Design of a highly efficient FeS2-based dual-heterojunction thin film solar cell

ABSTRACT This article demonstrates a highly efficient FeS2-based n-ZnSe/p-FeS2/p+-AlxGa1-xSb dual-heterojunction thin film solar cell using SCAPS-1D simulator. The study has been carried out taking the physical parameters from the literature. The influence of thickness, doping, and defect concentration of ZnSe, FeS2, and AlxGa1-xSb layers on the photovoltaic performance of the solar cell has been investigated in details. The power conversion efficiency (PCE) of the n-ZnSe/p-FeS2 single-heterojunction solar cell is ~23.22% with JSC = 47.52 mA/cm2, VOC = 0.59 V, and FF = 82.62%, respectively. The PCE of the solar cell further increases to ~36.75% with JSC = 48.13 mA/cm2, VOC = 0.94 V, and FF = 80.75%, respectively with the insertion of AlxGa1-xSb back surface field (BSF) layer. This increase in PCE is mainly due to the enhancement of VOC which is resulted from the suitable band alignment of the dual-heterojunction devices. These results indicate that FeS2-based dual-heterojunction thin film solar cell with ZnSe and AlxGa1-xSb window and BSF layers, respectively, is a potential candidate to fabricate high efficiency thin film solar cell for harvesting solar energy in the future.

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors-Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties.

Organic solar cells are on the dawn of the next era. The change of focus toward non-fullerene acceptors has introduced an enormous amount of organic n-type materials and has drastically increased the power conversion efficiencies of organic photovoltaics, now exceeding 18%, a value that was believed to be unreachable some years ago. In this Review, we summarize the recent progress in the design of ladder-type fused-ring non-fullerene acceptors in the years 2018–2020. We thereby concentrate on single layer heterojunction solar cells and omit tandem architectures as well as ternary solar cells. By analyzing more than 700 structures, we highlight the basic design principles and their influence on the optical and electrical structure of the acceptor molecules and review their photovoltaic performance obtained so far. This Review should give an extensive overview of the plenitude of acceptor motifs but will also help to understand which structures and strategies are beneficial for designing materials for highly efficient non-fullerene organic solar cells.

Prospect of single and coupled heterojunction solar cells based on n-MoS2 and n-WS2

A novel structure is proposed for single heterojunction solar cells based on n-type molybdenum disulfide (MoS2) and tungsten disulfide (WS2) deposited on p-type silicon substrate using thermal chemical vapor deposition. Moreover, the coupled heterostructures namely MoS2/WS2 and WS2/MoS2 are prepared by the same method. The main aim of this study is to evaluate the photovoltaic characteristics of the proposed heterojunction solar cells. For this purpose, various characterization techniques namely X-ray diffraction, field emission scanning electron microscopy, diffuse reflectance and Raman spectroscopies are employed. XRD patterns confirm MoS2 and WS2 layers form in hexagonal structures. Furthermore, DRS and Raman spectroscopy confirm the formation of few layers of MoS2, WS2, MoS2/WS2 and WS2/MoS2 heterostructures. The greatest power conversion efficiency (PCE) is obtained for the proposed solar cell fabricated based on MoS2 on p-type Si as single junction. This approach has suitable scientific input for application in photovoltaic cells and optoelectronic devices.

Theoretical DFT studies of Cu2HgSnS4 absorber material and Al:ZnO/ZnO/CdS/Cu2HgSnS4/Back contact heterojunction solar cell

We investigated a single heterojunction solar cell with stannite phase Cu2HgSnS4 as a new potential absorber material using the hybrid density functional theory for materials parameter and macroscopic device simulation studies for the photovoltaic response. The lattice constants are optimized using PBEsol and GGA exchange–correlation approach with mBJ parameterization and considering spin–orbit coupling effect on heavy element Hg, while strong correlation of Cu and Hg 3d electrons are taken into account by Hubbard parameter U = 0.52 Ry. The computed bandgap is ~1.33 eV. The effective mass of electrons and holes in the respective band edges (electron in conduction band and the hole in the valence band) is 0.25 m0 and 0.91 m0, respectively. Further, the computed materials optoelectronic parameters are used to optimize the device performance by introducing a variation in minority carrier lifetime, defect concentration in Cu2HgSnS4 absorber, Cu2HgSnS4/CdS interface, and the absorber thickness to achieve a realistic photovoltaic response. The optimal conversion efficiency is 11.6% after taking more realistic parameters in the considered single-junction solar cell. However, the maximum photovoltaic response >17% can be achieved by controlling absorber and interface defects together with optimal carrier concentration.

Theoretical evaluation of emerging Cd-free Cu3BiS3 based solar cells using experimental data of chemically deposited Cu3BiS3 thin films

The present research involves a combined experimental and theoretical study to evaluate the optoelectronic properties of Cu3BiS3 (CBS) semiconductor as an effective solar absorber in thin film photovoltaics. Our study consists of the synthesis and characterization of CBS films, followed by the execution of performance analysis as absorber material in a single heterojunction solar cell using numerical simulation by loading the individual material parameters for each layer of CBS solar cell into SCAPS-1D software. In the case of CBS layer, we considered the physical properties of CBS obtained experimentally in this work. The active layer was obtained by thermal diffusion of chemically deposited Bi2S3/CuS binary stacks at 300 °C and 350 °C in an inert atmosphere. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy studies confirm the appropriate composition as well as the formation of well-crystalline and single-phase orthorhombic Cu3BiS3 structure. Promising electrical properties were revealed by Hall effect measurements. The performance of the CBS layer was investigated considering the traditional CdS buffer layer and a Cd-free buffer layer such as Bi2S3. The higher conversion efficiency of 7.6% was obtained for CBS/Bi2S3 heterostructure compared with 6.8% efficiency using CdS buffer. A suitable band alignment at the CBS/Bi2S3 interface and ohmic back contact at Mo/CBS junction resulted to be mainly responsible for the enhanced efficiency.

Recent Advances in the Synthesis of Electron Donor Conjugated Terpolymers for Solar Cell Applications

The synthesis of donor (D)-acceptor (A) copolymers using structurally elaborated monomers is an active research field. Some of the challenges with the use of alternating D-A copolymers for photovoltaic applications are the relatively narrow absorption widths, the presence an absorption valleys in the visible region, unoptimized molecular energy levels and even lack of compatibility of the polymers with the common acceptors. The synthesis and characterization of polymers consisting of multiple chromophores (random and regular terpolymers) with complementing properties is currently gaining momentum in order to delicately optimize properties of polymers. A random terpolymer can either be of a system composed of one donor and two acceptors ((D-A1)-alt-(D-A2)) or a one acceptor and two donor segments ((D1-A)-alt-(D2-A)) incorporated in the polymer backbone. By varying the composition of the monomers in the feed of the polymerization reaction, the properties of the resulting terpolymers can be carefully optimized. Using this strategy, many materials with desired properties have been developed and power conversion efficiency (PCE) surpassing 14% in a single layer bulk heterojunction (BHJ) solar cell device have been reported. This review summarizes the most recent advances made in the development of terpolymers for organic photovoltaics (OPVs). The properties of the terpolymers are compared with those of reference binary polymers.

Simulation of CZTSSe single solar cells by AFORS-HET software

In this paper, this sthdy simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnSe4 absorber layer numerically using the AFORS-HET program .n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different absorption layer properties such as thickness, carrier concentration. The mixed zinc and cadmium sulphide (Cd1-X Zn X S) is hired as buffer layers and reseach of the effect its thickness. CdS was selected a buffer because it improves the interface with absorbent CZTSSe and has a lofty sending in the blue wavelength. at thickness =1 μm and acceptor concentration (Na=7.9×1015 cm-3) ,a maximum efficiency (η=11.9%) is provided with an open-circuit voltage (Voc=688mv), short-circuit current (Jsc=24.6 mA.cm-2) and fill factor (FF =70.8 of the CZTS solar cell, and Voc=(597 mv), Jsc= (41.7mA.cm-2), FF = (81.2 %) and η= (20.2%) of the CZTSe solar cell.

Novel Boron-Doped p-Type Cu2O Thin Films as a Hole-Selective Contact in c-Si Solar Cells.

p-type Cu2O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu2O and Cu2O:B films were deposited by rf magnetron sputtering, and the optical and electrical properties of the doped and undoped films were investigated. Boron doping enhanced the carrier concentration and the electrical conductivity of the Cu2O film. The band alignment of the Cu2O:B/Si heterojunction was investigated using XPS and UPS measurements. The Cu2O:B/Si interface has a valance band offset of 0.08 eV, which facilitates hole transport, and a conduction band offset of 1.35 eV, which blocks the electrons. A thin SiOx tunnel oxide interlayer was also explored as the passivation layer. The initial trials of incorporating this Cu2O:B layer as a hole transporting layer in a single heterojunction solar cell with the structure, ITO/Cu2O:B/n-Si/Ag, and a cell area of 1 cm2 yielded an open-circuit voltage of 370 mV, a short-circuit current density of 36.5 mA/cm2, and an efficiency of 5.4%. This p-type material could find potential applications in various optoelectronic applications like organic solar cells, TFTs, and LEDs.

Design Analysis of Heterojunction Solar Cells with Aligned AZO Nanorods Embedded in p-type Si wafer

Higher price-per-watt of silicon (Si) solar cells is still the main bottleneck in their widespread use for power generation due to their expensive manufacturing process. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell is one of the several methods being tried to replace conventional Si single homojunction solar cell technology. In this work, we have explored the possibility of producing photovoltaic materials by employing RF sputtering and hydrothermal technologies. Conductivity of ZnO nanorods has been increased by aluminium (Al) doping. The advantages of using Al doped ZnO (AZO) nanorods (NRs) have been investigated. The integrated reflectance (IR) has been found to be only ~2.86%. Hence, the short circuit current density (Jsc) has been increased by minimizing the reflection loss of solar cells. AZO NR array have been developed over several large area (3″ × 3″) textured p-Si wafers to confirm the repeatability. The maximum efficiency of AZO NRs/Si solar cell of 0.8 cm2 area has been found to be 6.25% for textured p-type Si wafer which is much higher than reported hitherto for this type of solar cell. A simple, low temperature, low cost procedure is thus being proposed, which has the potential of attaining lower cost of production of heterojunction silicon solar cells.

Electron Affinity and Bandgap Optimization of Zinc Oxide for Improved Performance of ZnO/Si Heterojunction Solar Cell Using PC1D Simulations

For further uptake in the solar cell industry, n-ZnO/p-Si single heterojunction solar cell has attracted much attention of the research community in recent years. This paper reports the influence of bandgap and/or electron affinity tuning of zinc oxide on the performance of n-ZnO/p-Si single heterojunction photovoltaic cell using PC1D simulations. The simulation results reveal that the open circuit voltage and fill factor can be improved significantly by optimizing valence-band and conduction-band off-sets by engineering the bandgap and electron affinity of zinc oxide. An overall conversion efficiency of more than 20.3% can be achieved without additional cost or any change in device structure. It has been found that the improvement in efficiency is mainly due to reduction in conduction band offset that has a significant influence on minority carrier current.

Effect of substrate off-orientation on the characteristics of GaInP/AlGaInP single heterojunction solar cells

The effects of GaAs substrate off-orientation on GaInP/AlGaInP heterojunction solar cells were investigated. The performances of solar cells fabricated on 2° and 10° off GaAs substrates were compared. The short circuit current densities were 10.44 mA/cm2 for the 10° off sample, 7.15 mA/cm2 and 7.41 mA/cm2 for the 2° off samples, which showed 30% higher short-circuit current density for 10° off samples. Also, 30% higher external quantum efficiencies and smooth surface morphology were observed in the solar cell fabricated on the 10° off GaAs substrate. Secondary ion mass spectrometry depth profiles showed that the solar cells on 2° off substrates had a 20-times higher oxygen concentration than the solar cells on 10° off GaAs substrate in the n-GaAs/GaAs buffer layer. The 30% reduction for the solar cells on 2° substrates in short circuit current density (Jsc) was attributed to the higher oxygen concentration of the 2° off samples than the 10° off samples. I-V characteristics comparison between different front contact grid patterns was also performed for optimization of grid contacts. A 0.47 V bandgap-voltage offset, one of the device performance figures of merit to compare PV cells with different materials, was obtained.

Theoretical studies of single and tandem Cu2ZnSn(S/Se)4 junction solar cells for enhanced efficiency

We simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnSe4 absorber layer numerically using one dimensional solar cell capacitance simulator (SCAPS-1D). n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different material layer properties such as thickness, carrier concentration, and defect density. First, the performance is optimized for the single junction solar cell with Mo as back contact material with `∼5 eV work function. A double junction CZTS/CZTSe tandem cell structure is realized keeping the same material properties as is used in the single CZTS and CZTSe solar cell simulation and flat band condition is considered at the interface for efficient carrier transport under matching current conditions. Tandem cell performance is determined after matching the current condition for top and bottom sub-cells. The CZTS/CZTSe short circuit current density is ∼20.98 mA/cm2 for current matched 211.33 nm thick CZTS top cell in conjunction with 2000 nm bottom cell. The maximum efficiency obtained under the flat band condition at the contact is ∼21.7% with open circuit voltage ∼1.324 V.

Combination of surface texturing and nanostructure coating for reduction of light reflection in ZnO/Si heterojunction thin film solar cell

In this study, we report a single heterojunction solar cell based on n-type zinc oxide/p-type silicon. Three different solar cells were fabricated based on ZnO thin film on Si substrate, ZnO nanorods on Si substrate, and ZnO nanorods on micro-pyramidal structure of Si substrate. The comparison between these three kinds of solar cells was studied. Pyramidal structure of silicon was fabricated using chemical etching technique of p-type Si (100). The chemical solution consists of NaOH, isopropyl alcohol and hydrazine hydrate. The results showed that Si micro-pyramids can enhance optical absorption of Si substrates by increasing surface area and entrapping of incident light. For fabrication of uniform ZnO nanorods, a seed layer of ZnO was deposited on Si substrates via radio frequency magnetron sputtering technique. This layer can be used as an active n-type material in heterojunction solar cells as well. ZnO nanostructures can increase light absorption due to their high specific surface area. The combination of ZnO nanorods and Si micro-pyramids can enhance light trapping effect and increase the efficiency of solar cells. The structural and morphology of samples were studied using field-emission scanning electron microscopy, atomic force microscopy and X-ray diffractometry while the optical properties were investigated using photoluminescence and reflectance spectrometry. The efficiency and fill factor of solar cells were obtained from current–voltage characteristics using a solar simulator and a source-meter. The results showed that the efficiency of solar cell based on nanostructures of ZnO/micropyramids of Si is highly increased due to high anti-reflective behavior of this sample.

Electrical Behavior of Solar Cell based on ZnO/PS

Because of high loss of photovoltaic conversion due to reflection of incident photon by the silicon surface, we proposed in this work a single heterojunction solar cell model based on porous silicon (PS) and Zinc oxide to minimize this loss, which the ZnO could act like front n-layer as well as antireflection coating saving processing cost and complexity. In the experiment the ZnO layer was deposited by spray pyrolysis method on porous silicon (PS) using nitrate precursors with different molar concentration. The proposed treatment has also demonstrated a significant decrease in the reflectivity of ZnO/PS. To simulate a solar cell based on porous silicon and zinc oxide, we have used PC1D software. The variation of internal and external quantum efficiency, and I-V characteristics have been done by changing the reflectivity of ARC layer, The I-V results obtained by PC1D simulation was compared with the experiment results: Simulations anticipated conversion efficiency was 14,5% while by experiments was 12% for the device fabricated with 0.25 M.

Inverted polymer solar cells with enhanced fill factor by inserting the potassium stearate interfacial modification layer

A thin potassium stearate (KSt) film combined with an optimized ZnO film was introduced to improve the fill factor (FF) of highly efficient inverted polymer solar cells (PSCs). Atomic force microscopy and contact angle measurements were used to show that the introduction of KSt did not change the morphology of interlayer. On the contrary, it is beneficial for the spread of the active layer on the interlayer. The origin of enhanced FF was systematically studied by the ideal current-voltage model for a single heterojunction solar cell and electrochemical impedance spectroscopy. On the basis of the data analysis, the reduced charge recombination loss was responsible for this improved FF. At last, when KSt was replaced by sodium stearate (NaSt), the similar experiment phenomenon was observed. This indicates that inserting a metallic stearate modified layer is a promising strategy to enhance inverted PSCs performance.

Synergistic photovoltaic–thermoelectric effect in a nanostructured CdTe/Bi2Te3 heterojunction for hybrid energy harvesting

A synergistic photovoltaic and thermoelectric effect takes place in a single heterojunction solar cell that consists of a p-type CdTe nanorod array and n-type Bi2Te3 nanostructures.

Versatile ternary organic solar cells: a critical review

Ternary organic solar cells enjoy both the enhanced light absorption by incorporating multiple organic materials in tandem solar cells and the simplicity of processing conditions that are used in single bulk heterojunction solar cells.